The present invention relates to an automatic sheet feeding apparatus, and more particularly, to an apparatus for stopping sheets at a predetermined position in a horizontal state and processing them, wherein the sheets are conveyed to the predetermined position, stopped there, and each sheet is processed and then returned to the predetermined position.
In order to copy a plurality of sets of an identical document consisting of a plurality of copies or originals (to be referred to as sheets hereinafter) in a conventional apparatus, a first sheet (actually the last page) is placed on a document table and is copied to produce a predetermined number of copies in a multicopying mode, a second sheet is then replaced with the first sheet and is copied similarly, and the third and subsequent sheets are sequentially placed on the document table to obtain a predetermined number of copies each. A stack of copies of the first sheet are stacked in the respective bins or the like, and then a stack of copies of the second sheet are overlayed on the respective first copies. The third or subsequent copies are respectively stacked on the immediately preceding ordered copies, thus obtaining a predetermined number of sets of an identical document. However, such copying and sorting is complicated and cumbersome.
In order to solve this problem, sorters are commercially available as conventional apparatuses for automatically sorting a plurality of sets of copies. However, when 20, 30 or more sets of copies must be sorted, a large space is inevitably required. Furthermore, removal of the sets of copies from the bins or the like is also time-consuming and cumbersome.
Recently, other conventional sorting apparatuses are proposed. In such apparatuses, a stack of sheets constituting a document are set on a stacker. A lowermost sheet of the stack is fed to a document table and is returned to the uppermost position of the stack after the copy operation. A currently lowermost sheet (the second lower sheet in the initial state) is fed to the document table and is returned onto the uppermost position after the copy operation. Every sheet is fed, copied and returned to the uppermost position in the same manner as described above, so that a single set of document copies is obtained. Subsequently, the above operation is repeated to obtain a predetermined number of sets of document copies. These apparatuses are described in Japanese Examined Patent Publication No. 50-34416, Japanese Unexamined Utility Model Publication No. 51-55445 and its entire specification, and Japanese Examined Patent Publication Nos. 55-27343 and 56-37536.
In reference to these apparatuses, strong demand has arisen for various types of apparatus for properly separating each sheet from the stacked sheets and feeding out the separated sheet.
For example, FIG. 1A shows a mechanism for feeding each sheet S from the lowermost position. A separation member 2 is urged against a feed roller 1, and the sheets fed by a convey roller 3 to the separation section are fed one by one.
In another conventional mechanism in FIG. 1B, a reverse rotation roller 4 is used in place of the separation member 2 in FIG. 1A.
In still another conventional mechanism in FIG. 1C, a reverse rotation belt 5 is used in place of the reverse rotation roller 4 in FIG. 1B.
In still another conventional mechanism in FIG. 1D, a reverse rotation roller 6 is disposed between two feed rollers 1A and 1B. A radial overlap distance d between the reverse rotation roller 6 and the feed rollers 1A and 1B is given to separate the sheets from each other utilizing rigidity of the sheets S.
In any of these examples, friction coefficients of the respective members satisfy the following condition: EQU .mu..sub.A &gt;.mu..sub.B &gt;.mu..sub.C
where
.mu..sub.A : the friction coefficient between the feed roller 1 and the sheet S PA1 .mu..sub.B : the friction coefficient between the sheet S and the separation members 2, 4, 5 and 6 PA1 .mu..sub.C : the friction coefficient between the opposing surfaces of two adjacent sheets
The sheets of the document are separated once in an SDF (Single Document Feeder) and an ADF (Automatic Document Feeder). However, the sheets of the document are repeatedly separated in an RDF (Recirculating Document Feeder), thus presenting the following problems.
(1) A separation member causes an identical sheet to wear since the separation member is always in tight contact with the sheet. In particular, when the content of the sheet S is written with a pencil and fed in the direction shown by an arrow in FIG. 2A, it smears or blurs since the separation member is always in slidable contact with the surface of the sheet. In the worst case, the content written with a pencil is partially erased.
(2) One of the separation members is held in the stationary state or continuously operated during the separation operation. The leading end of the sheet abuts against the separation member held in the stationary state when the sheet enters into the separation section, or the sheet receives a reaction force along a direction opposite to the convey direction. As shown in FIG. 2B, folds, turn-ups and wrinkles are then formed at the leading end of the sheet. In the worst case, the leading end of the sheet is torn.